The invention relates to an antenna coupling device for testing mobile telephones. An antenna coupler is a component of a test structure for servicing and development of mobile telephones.
When testing mobile telephones or mobiles, a plurality of properties or parameters are investigated, which can be loosely categorized as transmission and reception measurements. In transmission measurements for example, among other things a measurement of the phase error, of the frequency error, of the power and of the spectrum is carried out. In reception measurements bit error rates are measured. With respect to the technical background of tests of radio telephones, reference is made to chapters II and III of the book "GSM-Technik und Me.beta.praxis" by Siegmund Redl and Mathias Weber, Franzis-Verlag 2, second edition, Poing, 1995 from the series Funkschau Technik.
In order to enable measurement which approximates as closely as possible to practical use of the mobile telephone, the mobile telephone to be tested, (also named test item or DUT--device under test) should transmit and receive HF (=high frequency=radio frequency=RF) power via its antenna. If the transmission properties to the test item are known and sufficiently constant, the power received or transmitted by the test item can be calculated from the measured values. In the measuring method known per se with an antenna on the measuring appliance for coupling with the antenna of the test item, the measurement results are substantially influenced by the following parameters:
(i) space between both antennas; (ii) environment of the antennas (measuring appliances, laboratory installation, walls, people), due to reflections; (iii) interference from irradiating interfering transmitters; and (iv) HF properties of the antenna (radiation characteristics via solid angle and frequency).
Consequently measurements are only possible in large screened chambers, which are lined with HF-absorbent materials. Furthermore, the entire measuring apparatus must be located outside the chamber. In order to use the test item manually the person must enter the chamber and leave it again before measurement can be continued.
Miniature measuring chambers designed as boxes are also known in prior art. In these a basic disadvantage that in order to use the test item the box must be opened and closed again. Moreover, such a box is inconvenient, complex and expensive to manufacture. Transmission of the HF according to prior art is carried out in the interior of the box by a coupling mechanism, which is pushed over the antenna of the test item (model CB Z10 of Rohde and Schwarz), or by a dipole antenna with a coarse x- and y- positioning of the test item (model AH 5911 of ANDO) by mounting the test item on a co-ordinate system. In the first known type of transmission a disadvantage is that this is not suitable for test items with an antenna integrated in the casing or with an antenna too large for the coupling mechanism. In the second type, positioning of the test item is imprecise, as the latter cannot be securely fixed. Finally, in both known types of HF transmission the frequency range of the coupler is restricted to an undesirable degree by the structure, and the coupling attenuation for many test items is so high that the dynamics of the measuring appliance are not sufficient.